Process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate and its use

ABSTRACT

The present invention refers to a process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate and its uses. The process may be carried out in a reactor system comprising a tank ( 1 ) equipped with a stirrer ( 2 ), at least one filtering device ( 4 ) and a grinding device ( 18 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase of PCT Application No.PCT/EP2013/051884, filed Jan. 31, 2013, which claims priority toEuropean Application No. 12153898.7, filed Feb. 3, 2012 and U.S.Provisional Application No. 61/597,193, filed Feb. 10, 2012.

The invention relates to the field a process producing aqueous earthalkali hydrogen carbonate solution and the use of such solutions.

Calcium carbonate is used extensively in the paper industry as a fillercomponent in paper. It is a low cost, high brightness filler used toincrease sheet brightness and opacity. Its use has increaseddramatically in the last decades due to the conversion from acid toalkaline papermaking at paper mills. Both natural and synthetic calciumcarbonates are used in the paper industry. Natural carbonate, orlimestone, is ground to a small particle size prior to its use in paper,while synthetic calcium carbonate is manufactured by a precipitationreaction and is therefore called precipitated calcium carbonate (PCC).

Besides its use in the papermaking industry, precipitated calciumcarbonate is also used for various other purposes, e.g. as filler orpigment in the paint industries, and as functional filler for themanufacture of plastic materials, plastisols, sealing compounds,printing inks, rubber, toothpaste, cosmetics, food, pharmaceuticals etc.

Precipitated calcium carbonate exists in three primary crystallineforms: calcite, aragonite and vaterite, and there are many differentpolymorphs (crystal habits) for each of these crystalline forms. Calcitehas a trigonal structure with typical crystal habits such asscalenohedral (S-PCC), rhombohedral (R-PCC), hexagonal prismatic,pinacoidal, colloidal (C-PCC), cubic, and prismatic (P-PCC). Aragoniteis an orthorhombic structure with typical crystal habits of twinnedhexagonal prismatic crystals, as well as diverse assortment of thinelongated prismatic, curved bladed, steep pyramidal, chisel shapedcrystals, branching tree, and coral or worm-like form.

Usually, PCC is prepared by introducing CO₂ into an aqueous suspensionof calcium hydroxide, the so-called milk of limeCa(OH)₂+CO₂→CaCO₃+H₂O.

There are numerous patent applications known to the person skilled inthe art that describe the preparation of precipitated calcium carbonate.One of them is EP 1 966 092 B1, where the obtained precipitated calciumcarbonate is only a by-product of the sequestration of CO₂. Another oneis WO 2010/12691, this document disclosing the production of PCC by theaddition of an earth alkali hydroxide to water that contains earthalkali ions.

International Patent Application WO 2006/008242 A1, for example,describes the production of high purity calcium carbonate or magnesiumcarbonate from a feedstock comprising a Ca- or Mg-comprising mixed metaloxide, wherein the feedstock is contacted with a CO₂ containing gas inorder to sequestrate the CO₂ and in a further step the high puritycalcium carbonate or magnesium carbonate is precipitated from theaqueous solution that resulted from contacting the feedstock with theCO₂.

In addition to the above-mentioned fields, calcium carbonate can also beused in the field of the treatment and mineralization of water.

Drinking water has become scarce. Even in countries that are rich inwater, not all sources and reservoirs are suitable for the production ofdrinking water, and many sources of today are threatened by a dramaticdeterioration of the water quality. Initially feed water used fordrinking purposes was mainly surface water and groundwater. However thetreatment of seawater, brine, brackish waters, waste waters andcontaminated effluent waters is gaining more and more importance forenvironmental and economic reasons.

In order to recover water from seawater or brackish water, for potableusages, several processes are known, which are of considerableimportance for dry areas, coastal regions and sea islands, and suchprocesses comprise distillation, electrolytic as well as osmotic orreverse osmotic processes. The water obtained by such processes is verysoft and has a low pH value because of the lack of pH-buffering salts,and thus, tends to be highly reactive and unless treated, it can createsevere corrosion difficulties during its transport in conventionalpipelines. Furthermore, untreated desalinated water cannot be useddirectly as a source of drinking water. To prevent the dissolution ofundesirable substances in pipeline systems, to avoid the corrosion ofwater works such as pipes and valves and to make the water palatable, itis necessary to mineralize the water.

Conventional processes that are mainly used for the mineralization ofwater are lime dissolution by carbon dioxide and limestone bedfiltration. Other, less common remineralization processes, comprise,e.g., the addition of hydrated lime and sodium carbonate, the additionof calcium sulfate and sodium bicarbonate, or the addition of calciumchloride and sodium bicarbonate.

The lime process involves treatment of lime solution with CO₂ acidifiedwater, wherein the following reaction is involved:Ca(OH)₂+2CO₂→Ca²⁺+2HCO₃ ⁻

As can be gathered from the above reaction scheme, two equivalents ofCO₂ are necessary to convert one equivalent of Ca(OH)₂ into Ca²⁺ andbicarbonate for remineralization. This method is dependent on theaddition of two equivalents of CO₂ in order to convert the alkalinehydroxide ions into the buffering species HCO₃ ⁻. For theremineralization of water, a saturated calcium hydroxide solution,commonly named lime water, of 0.1-0.2 wt.-% based on the total weight,is prepared from a lime milk (usually at most 5 wt.-%). Therefore, asaturator to produce the lime water must be used and large volumes oflime water are necessary to achieve the target level ofremineralization. A further drawback of this method is that hydratedlime is corrosive and requires appropriate handling and specificequipment. Furthermore, a poorly controlled addition of hydrated lime tothe soft water can lead to unwanted pH shifts due to the absence ofbuffering properties of lime.

The limestone bed filtration process comprises the step of passing thesoft water through a bed of granular limestone dissolving the calciumcarbonate in the water flow. Contacting limestone with CO₂ acidifiedwater mineralizes the water according to:CaCO₃+CO₂+H₂O→Ca²⁺+2HCO₃ ⁻

Unlike the lime process, only one equivalent of CO₂ is stochiometricallynecessary to convert one equivalent of CaCO₃ into Ca²⁺ and bicarbonatefor remineralization. Moreover, limestone is not corrosive and due tothe buffering properties of CaCO₃ major pH shifts are prevented.

One additional advantage of the use of calcium carbonate compared tolime is its very low carbon dioxide footprint. In order to produce onetonne of calcium carbonate 75 kg of CO₂ is emitted, whereas 750 kg ofCO₂ is emitted for the production of one tonne of lime. Therefore, theuse of earth alkali carbonates such marble, dolomite or only have burneddolomite instead of lime presents some environmental benefits.

The dissolution rate of granular calcium carbonate, however, is slow andfilters are required for this process. This induces a sizeable footprintof these filters and large plant surfaces are required for the limestonebed filtration systems.

Methods for remineralization of water using lime milk or a slurry oflime are described in U.S. Pat. No. 7,374,694 and EP 0 520826. U.S. Pat.No. 5,914,046 describes a method for reducing the acidity in effluentdischarges using a pulsed limestone bed.

WO 2010/12691 discloses a process for the treatment of water containingat least calcium and/or magnesium salts through membranes of reverseosmosis typ. The process comprises at least one step of recovering waterthat is at least partly desalinated, a step of recovering a concentrateoriginating from the membranes and that contains bicarbonates, a step ofinjecting CO₂ or an acid into the at least partially desalinated water,and a step of remineralization of the at least partially desalinatedwater. The CO₂ is added to the bicarbonate solution in order todecarbonate the concentration and to form agglomerates of calciumcarbonates out of the bicarbonates.

The applicant also knows the following unpublished European PatentApplications in the field of water treatment.

European Patent Application 11 175 012.1 describes a method for theremineralization of desalinated and fresh water containing a certaincarbon dioxide level by injecting a micronized calcium carbonate slurryin feed water.

European Patent Application 10 172 771.7 describes a method for theremineralization of desalinated and fresh water by injecting amicronized calcium carbonate slurry.

Finally, European Patent Application 11 179 541.5 describes a method forthe remineralization of water by combining a calcium carbonate solutionand feed water.

In the three unpublished European Patent Applications of the field ofwater treatment no indication is given about the specific surface area(SSA) of the earth alkali carbonates used. From the mean particle sizereferred to in the examples of these patent applications it is notpossible to calculate the specific surface area (SSA) of thecorresponding products. No indication is given with regard to theinfluence of the specific surface area on an efficient production of anearth alkali carbonate solution.

Also, no indication is given with respect to a parallel in situ particledividing in order to improve the process.

Thus, considering the drawbacks of the known processes formineralization or remineralization of water, it is the object of thepresent invention to provide an alternative and improved process formineralization of water.

Another object of the present invention is to provide a process formineralization of water that does not require a corrosive compound, andthus, avoids the danger of incrustation, eliminates the need forcorrosion resistant equipment, and provides a safe environment forpeople working in the plant. It would also be desirable to provide aprocess that is environmental friendly and requires low amounts ofcarbon dioxide when compared to today's water remineralization with limeprocesses.

Another object of the present invention is to provide a process formineralization of water, wherein the amount of minerals can be adjustedto the required values.

The foregoing and other objects are solved by the provision of a processfor the preparation of an aqueous solution comprising at least one earthalkali hydrogen carbonate, the process comprising the steps of:

-   a) providing water,-   b) providing at least one substance comprising at least one earth    alkali carbonate and optionally at least one earth alkali hydroxide    in a minor amount in respect to earth alkali carbonate, the at least    one substance being in a dry form or in an aqueous form,-   c) providing CO₂,-   d) combining either:    -   (i) the water of step a), the at least one substance comprising        at least one earth alkali carbonate and the optional at least        one earth alkali hydroxide of step b) and the CO₂ of step c), or    -   (ii) the water of step a) and the at least one substance        comprising at least one earth alkali carbonate and the optional        at least one earth alkali hydroxide of step b) in order to        obtain an alkaline aqueous suspension of the at least one        substance comprising at least one earth alkali carbonate and the        optional at least one earth alkali hydroxide, and subsequently        combining the alkaline aqueous suspension with the CO₂ of step        c)    -   in order to obtain a resulting suspension S having a pH of        between 6 and 9, the resulting suspension S containing        particles,-   e) filtering at least a part of the resulting suspension S by    passing at least a part of the resulting suspension S through a    filtering device in order to obtain the aqueous solution comprising    at least one earth alkali hydrogen carbonate,-   f) subjecting at least a part or all of the particles of the    resulting suspensions S to a particle dividing step,    wherein step f) can take place before and/or parallel to and/or    after step e),    wherein the particles of the resulting suspension S that is obtained    in step d) represent a total particle surface area (SSA_(total))    that is at least 1 000 m²/tonne of the resulting suspension S, and    with the proviso that an addition of the CO₂ of step c) does not    take place before an addition of the at least one substance    comprising at least one earth alkali carbonate and the optional at    least one earth alkali hydroxide of step b).

When the specific surface area of the substance comprising at least oneearth alkali carbonate and the optional at least one earth alkalihydroxide is known, then the total particle surface of the alkalineaqueous suspension of step d) can be easily adjusted. Alternatively, thespecific surface area of the substance comprising at least one earthalkali carbonate and the optional at least one earth alkali hydroxidehas to be determined by the method that is known to the person skilledin the art and that is laid down in Standard ISO 9277.

According to another aspect of the present invention, use of an aqueoussolution comprising at least one earth alkali hydrogen carbonate for theproduction of a precipitated earth alkali carbonate, and in particularfor the production of a precipitated calcium carbonate is provided.

According to yet another aspect of the present invention, use of anaqueous solution comprising at least one earth alkali hydrogen carbonatefor the production of precipitated hydromagnesite is provided.

According to further aspect of the present invention, use of an aqueoussolution comprising at least one earth alkali hydrogen carbonate for themineralization of water is provided.

Yet to another aspect of the present invention there is a process forthe mineralization of water provided, the process comprising thefollowing steps:

-   I) providing feed water,-   II) providing an aqueous solution comprising at least one earth    alkali hydrogen carbonate, and-   III) combining the feed water of step I) and the aqueous solution    comprising at least one earth alkali hydrogen carbonate of step II)    in order to obtain mineralized water.

Yet another aspect of the invention is a process for the production of aprecipitated earth alkali carbonate, the process comprising thefollowing steps:

-   IV) providing an aqueous solution comprising at least one earth    alkali hydrogen carbonate, and-   V) heating the aqueous solution comprising at least one earth alkali    hydrogen carbonate of step IV) in order to obtain the precipitated    earth alkali carbonate and/or-   VI) adding at least one earth alkali hydroxide or earth alkali oxide    to the solution of step IV) to obtain the precipitated earth alkali    carbonate.

Advantageous embodiments of the present invention are defined in thecorresponding sub-claims.

According to one embodiment of the present invention, the particles ofthe resulting suspension S represent a total particle surface area(SSA_(total)) that is in the range of 5 000-5 000 000 m²/tonne of theresulting suspension S, preferably in the range of 10 000 to 5 000 000m²/tonne of the resulting suspension S, and more preferably in the rangeof 70 000-500 000 m²/tonne of the resulting suspension S, for example100 000 to 500 000 m²/tonne.

According to another embodiment, the at least one substance comprisingat least one earth alkali carbonate and the optional at least one earthalkali hydroxide of step b) is selected from the group comprisingmarble, limestone, chalk, half burnt lime, burnt lime, dolomiticlimestone, calcareous dolomite, half burnt dolomite, burnt dolomite, andprecipitated earth alkali carbonates such as precipitated calciumcarbonate, for example of calcitic, aragonitic and/or vateritic mineralcrystal structure, for example from water de-hardening by the additionof Ca(OH)₂. The use of marble, limestone, chalk and dolomite ispreferred because they are naturally occurring minerals and theturbidity of the final drinking water quality is guaranteed by using aclear aqueous solution comprising at least one earth alkali hydrogencarbonate that is produced using these naturally occurring minerals.Natural marble deposits are mostly containing acid insoluble silicateimpurities. However, such acid insoluble, sometimes colored silicates donot affect the final water quality with respect of turbidity when usingthe product that is prepared by the inventive process.

In addition, suspensions or solutions prepared by using naturallyoccurring minerals such as marble, limestone, chalk or dolomite arecontaining essential healthy trace elements improving the quality ofdrinking water.

The optional at least one earth alkali hydroxide is preferably calciumhydroxide and/or magnesium hydroxide. Due to the fact of very lowsolubility of Mg(OH)₂ in water compared to Ca(OH)₂ the speed of reactionof Mg(OH)₂ with CO₂ is very limited and in presence of Ca(OH)₂ insuspension the reaction of CO₂ with Ca(OH)₂ is very much preferred.Surprisingly, by using the inventive process it is possible to produceMg(HCO₃)₂ rich earth alkali hydrogen carbonate suspension also inpresence of Ca(OH)₂ in the suspension.

According to another embodiment the at least one substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide of step b) has a weight median particle size (d₅₀) inthe range of 0.1 μm to 1 mm, and preferably in the range of 0.7 μm to100 μm.

The at least one substance comprising at least one earth alkalicarbonate and the optional at least one earth alkali hydroxide of stepb) has preferably a specific surface area in the range of 0.01 to 200m²/g, and more preferably in the range of 1 to 100 m²/g, for example 1to 15 m²/g.

The term “specific surface area (SSA)” in the meaning of the presentinvention describes the material property of pigments/minerals/solidsthat measures the surface area per gram of pigments. The unit is m²/g.

The term “total particle surface area (SSA_(total))” in the meaning ofthe present invention describes the total surface area per tonne ofsuspension S.

In a preferred embodiment of the present invention, the at least onesubstance comprising at least one earth alkali carbonate and theoptional at least one earth alkali hydroxide of step b) has ahydrochloric acid (HCl) insoluble content from 0.02 to 90 wt.-%,preferably from 0.05 to 15 wt.-%, based on the total weight of the drysubstance. The HCl insoluble content may be, e.g., minerals such asquartz, silicate, mica a/o pyrite.

According to yet another embodiment of the present invention, theresulting suspension S that is obtained in step d) has a solids contentin the range from 0.1 to 80 wt.-%, preferably in the range of 3 to 50wt.-%, more preferably in the range of 5 to 35 wt.-%, based on the totalweight of the resulting suspension S.

The water of step a) is preferably selected from distilled water, tapwater, desalinated water, brine, treated wastewater or natural watersuch as ground water, surface water or rainfall. It can also containbetween 10 and 2 000 mg NaCl per liter.

According to one embodiment of the present invention the CO₂ is selectedfrom gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxideor a gaseous mixture of carbon dioxide and at least one other gas, andis preferably gaseous carbon dioxide. When the CO₂ is a gaseous mixtureof carbon dioxide and at least one other gas, then the gaseous mixtureis a carbon dioxide containing flue gas exhausted from industrialprocesses like combustion processes or calcination processed or alike.CO₂ can also be produced by reacting an alkali- and/or earth alkalicarbonate with acid. Furthermore, it can be produced by the combustionof organics, such as ethyl alcohol, wood and the like, or byfermentation. When a gaseous mixture of carbon dioxide and at least oneother gas is used, then the carbon dioxide is present in the range of 8to about 99% by volume, and preferably in the range of 10 to 25% byvolume, for example 20% by volume. According to a very preferredembodiment, the CO₂ is pure gaseous CO₂ with a purity of >99%, e.g. apurity of >99.9%.

In the light of an ecological concept, it is desirable to follow as faras possible the Kyoto protocol on the reduction of combustion ofpetrochemical sources and to reduce petrochemical derived CO₂ so thatthe CO₂ used for the process has a ¹⁴C to ¹²C decay of at least 500,more preferred at least 800, most preferred at least 850 to 890 decayper h and per g of C in the CO₂.

Following the Kyoto protocol, it is also desirable that at least a partor all of the electrical power used in the process of the presentinvention is derived from solar power, for example from thermal and/orvoltammetry solar panels.

In a further preferred embodiment of the present invention following theKyoto protocol, the amount of CO₂ used, in mol, to produce 1 mol of theat least one earth alkali hydrogen carbonate in the aqueous solution isin the range of only 0.5 to 4 mol, preferably in the range of only 0.5to 2.5 mol, more preferably in the range of only 0.5 to 1.0 mol, andmost preferably in the range of only 0.5 to 0.65 mol.

The process according to the present invention contains a step f),wherein all or a part of the resulting suspension S is subjected to aparticle dividing step of the particles that are contained in theresulting suspension S. The particle dividing step f) can take placebefore step e), parallel to step e), after step e) or before and afterstep e). In a preferred embodiment the particle dividing step f) is agrinding and/or crushing step, and is most preferably a grinding step.This step provides the benefit that the (chemical) reaction speed of theinventive process is increased by continuously producing a freshlyprepared and hence active surface of the substance comprising at leastone earth alkali carbonate and the optional at least one earth alkalihydroxide. In addition, this process step decreases the size ofparticles of the substance comprising the earth alkali carbonate and theoptional at least one earth alkali hydroxide of step b), and thusenables a continuous operation of the process.

The term “crushing” in the meaning of the present invention is used whenthe feed material that is subjected to this step is in the centimeter(cm) range, for example 10 cm.

The term “grinding” in the meaning of the present invention is used whenthe feed material that is subjected to this step is in the millimeter(mm) or nanometer (nm) range, for example 10 mm.

According to another preferred embodiment of the invention the aqueoussolution comprising at least one earth alkali hydrogen carbonate that isobtained in step e) or step f) has a hardness from 5 to 130° dH,preferably from 10 to 60° dH, and most preferably from 15 to 50° dH.

For the purpose of the present invention the hardness refers to theGerman hardness and is expressed in “degree German hardness, ° dH”. Inthis regard, the hardness refers to the total amount of earth alkaliions in the aqueous solution comprising the earth alkali hydrogencarbonate, and it is measured by complexometric titration at pH 10 usingethylene-diamine-tetra-actetic acid (EDTA) and Eriochrome T asequivalent point indicator.

The aqueous solution comprising at least one earth alkali hydrogencarbonate and that is obtained in step e) or step f) has preferably a pHin the range of 6.5 to 9, preferably in the range of 6.7 to 7.9, andmost preferably in the range of 6.9 to 7.7, at 20° C.

According to one embodiment of the present invention, the aqueoussolution comprising at least one earth alkali hydrogen carbonate andthat is obtained in step e) or step f) has a calcium concentration, ascalcium carbonate, from 1 to 700 mg/l, preferably from 50 to 650 mg/l,and most preferably from 70 to 630 mg/l. According to another embodimentthe aqueous solution comprising at least one earth alkali hydrogencarbonate and that is obtained in step e) or step f) has a magnesiumconcentration, as magnesium carbonate from 1 to 200 mg/l, preferablyfrom 2 to 150 mg/l, and most preferably from 3 to 125 mg/l.

According to still another embodiment of the present invention theaqueous solution comprising at least one earth alkali hydrogen carbonateand that is obtained in step e) or step f) has a turbidity value oflower than 1.0 NTU, preferably of lower than 0.5 NTU, and mostpreferably of lower than 0.3 NTU.

It is preferred that at least step d) is carried out at a temperaturethat is in a range of 5 to 55° C., and preferably in a range of 20 to45° C.

According to an even more preferred embodiment of the present inventionthe aqueous solution obtained in step e) or optional step f) comprises:

-   (x) a calcium hydrogen carbonate, preferably with a calcium    concentration of 25 to 150 mg/l, as calcium carbonate, or-   (xx) a magnesium hydrogen carbonate, preferably with a magnesium    concentration of >0 to 50 mg/l, or-   (xxx) a mixture of a calcium and a magnesium hydrogen carbonate,    preferably in a total calcium and magnesium concentration of 25 to    200 mg/l, as calcium carbonate and magnesium carbonate.

According to a most preferred embodiment of the present invention theaqueous solution obtained in step e or optional step f) comprises:

a calcium hydrogen carbonate with a calcium concentration of 45 mg/l, ascalcium carbonate, or

a mixture of a calcium and a magnesium hydrogen carbonate with a calciumconcentration of 80 to 120 mg/l, as calcium carbonate, and a magnesiumconcentration of 20 to 30 mg/l, as magnesium carbonate.

A mixture of calcium and a magnesium hydrogen carbonate can be obtainedwhen dolomite, half burned and/or fully burned dolomite containingmaterial is used as the substance comprising the earth alkali carbonate.In the meaning of the present invention burned dolomite comprisescalcium oxide (CaO) and magnesium oxide (MgO), whereas half burntdolomite comprises Mg in the form of magnesium oxide (MgO) and Ca in theform of calcium carbonate (CaCO₃), but can also include some minoramount of calcium oxide (CaO).

In a preferred embodiment of the present invention the process is acontinuous process. However, the process of the present invention canalso be carried out in a semi-batch mode. In this case, the resultingsuspension S can, for example, represent a total particle surface thatis around 1 000 000 m²/tonne and is subjected to the process of thepresent invention. Then, the product, i.e. the aqueous solution of theearth alkali hydrogen carbonate, is discharged from the process untilthe remaining resulting suspension S represents a total particle surfacethat is around 1 000 m²/tonne, and then a new amount of the at least onesubstance comprising at least one earth alkali carbonate and theoptional at least one earth alkali hydroxide in a minor amount inrespect to the earth alkali carbonate is introduced into the process. Itis noted that the total particle surface can be determined during eachpoint of the continuous process by determining the specific surface area(SSA) of the suspension S as well as the dry content of the suspensionS.

Most preferably, the continuous process is controlled by the amount ofdischarged aqueous solution comprising at least one earth alkalihydrogen carbonate and the measurement of the solid content ofsuspension S or by complexometric titration or by measurement of theconductivity of the earth alkali hydrogen carbonate solution.

In yet another embodiment of the present invention the filtering deviceof step e) is a membrane filter, such as for example a microfiltrationand/or an ultrafiltration membrane. In a preferred embodiment, thefiltering device of step e) is a tube membrane filter with a pore sizeof between 0.02 μm and 0.5 μm, and preferably of between 0.05 and 0.2μm. Preferred are platy and/or tube filters. The tube filters havepreferably an inner tube diameter of 0.1 to 10 mm, and more preferablyof 0.1 to 5 mm. In a preferred form the membranes are of sinteredmaterial, porous porcelain or synthetic polymers, such as polyethylene,Teflon® or the like.

A further object of the present invention is the use of an aqueoussolution comprising at least one earth alkali hydrogen carbonateobtained by the inventive process for the production of a precipitatedearth alkali carbonate and/or hydromagnesite, and in particular for theproduction of a precipitated calcium carbonate and/or hydromagnesite.Such precipitated earth alkali carbonates, and in particular aprecipitated calcium carbonate and hydromagnesite are useful as fillersin many industrial applications, for example as fillers in paper, paintor plastic.

Another object of the present invention is the use of an aqueoussolution comprising at least one earth alkali hydrogen carbonateobtained by the inventive process for the mineralization of water.

A further object of the present invention is a process for themineralization of water comprising the following steps: I) providingfeed water, II) providing an aqueous solution comprising at least oneearth alkali hydrogen carbonate, and III) combining the feed water ofstep I) and the aqueous solution comprising at least one earth alkalihydrogen carbonate of step II) in order to obtain mineralized water.

According to one embodiment of the process for the mineralization ofwater the aqueous solution comprising at least one earth alkali hydrogencarbonate of step II) has a hardness that is at least 3° dH, andpreferably at least 5° dH higher than the hardness of the feed water ofstep I).

According to a preferred embodiment, the aqueous solution comprising theat least one earth alkali hydrogen carbonate of step II) has a hardnessof at least 15° dH.

According to another embodiment of the process for the mineralization ofwater the mineralized water has a calcium concentration, as calciumcarbonate, from 1 to 700 mg/l, preferably from 50 to 650 mg/l, and mostpreferably from 70 to 630 mg/l. According to yet another embodiment ofthe process for the mineralization of water the mineralized water has amagnesium concentration, as magnesium carbonate, from 1 to 200 mg/l,preferably from 2 to 150 mg/l, and most preferably from 3 to 125 mg/l.

An even further object of the present invention is a process for theproduction of a precipitated earth alkali carbonate, the processcomprising the following steps:

-   IV) providing an aqueous solution comprising at least one earth    alkali hydrogen carbonate, and-   V) heating the aqueous solution comprising at least one earth alkali    hydrogen carbonate of step IV) in order to obtain the precipitated    earth alkali carbonate, and/or-   VII) adding at least one earth alkali hydroxide or earth alkali    oxide to the solution of step IV) to obtain the precipitated earth    alkali carbonate.

By heating the aqueous solution comprising at least one earth alkalihydrogen carbonate, water is evaporated from the solution and upon acertain point of time the earth alkali carbonate starts to precipitateout of the solution.

According to a preferred embodiment of the process for the production ofa precipitate earth alkali carbonate, the precipitated earth alkalicarbonate is selected from among an amorphous earth alkali carbonate,such as amorphous calcium carbonate or magnesium carbonate, crystallinecalcium carbonate in the calcitic, the aragonitic or the vateritic form,magnesite and hydromagnesite, or is a mixture of the aforementioned.

“Conductivity” in the meaning of the present invention is used as aninverse indicator of how salt-free, ion-free, or impurity-free themeasured water is; the purer the water, the lower the conductivity. Theconductivity can be measured with a conductivity meter and is specifiedin S/m.

“Ground calcium carbonate (GCC)” in the meaning of the present inventionis a calcium carbonate obtained from natural sources including marble,chalk or limestone, and processed through a treatment such as grinding,screening and/or fractionizing by wet and/or dry, for example, by acyclone.

“Precipitated calcium carbonate (PCC)” in the meaning of the presentinvention is a synthesized material, generally obtained by precipitationfollowing the reaction of carbon dioxide and lime in an aqueousenvironment or by precipitation of a calcium and carbonate source inwater or by precipitation of calcium and carbonate ions, for exampleCaCl₂ and Na₂CO₃, out of solution. Precipitated calcium carbonate existsin three primary crystalline forms: calcite, aragonite and vaterite, andthere are many different polymorphs (crystal habits) for each of thesecrystalline forms. Calcite has a trigonal structure with typical crystalhabits such as scalenohedral (S-PCC), rhombohedral (R-PCC), hexagonalprismatic, pinacoidal, colloidal (C-PCC), cubic, and prismatic (P-PCC).Aragonite is an orthorhombic structure with typical crystal habits oftwinned hexagonal prismatic crystals, as well as a diverse assortment ofthin elongated prismatic, curved bladed, steep pyramidal, chisel shapedcrystals, branching tree, and coral or worm-like forms.

Throughout the present document, the “particle size” of a calciumcarbonate product is described by its distribution of particle sizes.The value d_(x) represents the diameter relative to which x % by weightof the particles have diameters less than d_(x). This means that the d₂₀value is the particle size at which 20 wt.-% of all particles aresmaller, and the d₇₅ value is the particle size at which 75 wt.-% of allparticles are smaller. The d₅₀ value is thus the weight median particlesize, i.e. 50 wt.-% of all grains are bigger or smaller than thisparticle size. For the purpose of the present invention the particlesize is specified as weight median particle size d₅₀ unless indicatedotherwise. These values were measured using a Mastersizer 2000 devicefrom the company Malvern Instruments GmbH, Germany.

The term “mineralization” as used in the present invention refers to theincrease of essential mineral ions in water not containing minerals atall or in insufficient amount to obtain water that is palatable. Amineralization can be achieved by adding at least calcium carbonate tothe water to be treated. Optionally, e.g., for health-related benefitsor to ensure the appropriate intake of some other essential mineral ionsand trace elements, further substances may be mixed to the calciumcarbonate and then added to the water during the remineralizationprocess. According to the national guidelines on human health anddrinking water quality, the remineralized product may compriseadditional minerals containing magnesium, potassium or sodium, e.g.,magnesium carbonate, magnesium sulfate, potassium hydrogen carbonate,sodium hydrogen carbonate or other minerals containing essential traceelements.

Useful substances for the use in the inventive process for preparing anaqueous solution comprising at least one earth alkali hydrogen carbonateare natural calcium and/or magnesium carbonate containing inorganicsubstances or salts, or synthetic calcium and/or magnesium carbonatecontaining inorganic substances or salts.

Useful natural occurring inorganic substances are for example marble,limestone, chalk, dolomitic marble and/or dolomite. Synthetic substancesare for example precipitated calcium carbonates in the calcitic,aragonitic and/or vateritic crystalline form. However, natural occurringinorganic substances are preferred because they inherently contain someessential trace elements.

“Turbidity” in the meaning of the present invention describes thecloudiness or haziness of a fluid caused by individual particles(suspended solids) that are generally invisible to the naked eye. Themeasurement of turbidity is a key test of water quality and can becarried out with a nephelometer. The units of turbidity from acalibrated nephelometer as used in the present invention are specifiedas Nephelometric Turbidity Units (NTU).

The inventive process for the preparation of an aqueous solutioncomprising at least one earth alkali hydrogen carbonate comprises thesteps of: a) providing water, b) providing at least one substancecomprising at least one earth alkali carbonate and optionally at leastone earth alkali hydroxide in a minor amount in respect to the earthalkali carbonate, the at least one substance being in a dry form or inan aqueous form, c) providing CO₂, d) combining either: (i) the water ofstep a), the at least one substance comprising at least one earth alkalicarbonate and the optional at least one earth alkali hydroxide of stepb) and the CO₂ of step c), or (ii) the water of step a) and the at leastone substance comprising at least one earth carbonate and the optionalat least one earth alkali hydroxide of step b) in order to obtain analkaline aqueous suspension of the at least one substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide, and subsequently combining the alkaline aqueoussuspension with the CO₂ of step c) in order to obtain a resultingsuspension S having a pH of between 6 and 9, the resulting suspension Scontaining particles, e) filtering at least a part of the resultingsuspension S by passing at least a part of the resulting suspension Sthrough a filtering device in order to obtain the aqueous solutioncomprising at least one earth alkali hydrogen carbonate, f) subjectingat least a part of the particles of the resulting suspension S to aparticle dividing step, wherein step f) can take place before and/orparallel to and/or after step e), wherein the particles of the resultingsuspension S that is obtained in step d) represent a total particlesurface area (SSA_(total)) that is at least 1 000 m²/tonne of theresulting suspension S, and with the proviso that an addition of the CO₂of step c) does not take place before an addition of the at least onesubstance comprising at least one earth alkali carbonate and theoptional at least one earth alkali hydroxide of step b).

The process according to the present invention is preferably carried outin a reactor system that comprises at least a tank, at least onefiltering device, and means connecting the tank and the at least onefiltering device, such as pipes or tubes. In addition, the reactorsystem can also comprise measurement equipment, such as pressure,temperature, pH, turbidity measuring units, and the like.

The tank is equipped with a stirrer, at least one inlet for the water,the carbon dioxide and the substance comprising at least one earthalkali carbonate and the optional at least one earth alkali hydroxide.Connected to the tank, there is also a filtering device where at least apart of the resulting suspension S having a pH of between 6 and 9 andthat is prepared in the tank is passed through in order to obtain theaqueous solution comprising at least one earth alkali hydrogencarbonate.

Additionally, the reactor system contains a dividing device (particlesize reduction device) that is assembled in a parallel or serialarrangement with regard to the filtering device or is introduced in tothe tank. The tank is connected to the crushing and/or grinding devicewhere at least a part of the particles contained in the resultingsuspension S are subjected to a particle size reduction. The grindingand/or crushing device can be arranged in such a way that only a part ofthe resulting suspension S that is contained in the tank passes throughthe crushing and/or grinding device before circulating back into thetank (“parallel arrangement”), or it can be arranged in line (serial)with the filtering device, so that all of the resulting suspension Sthat passes the crushing and/or grinding device will be filteredsubsequently in the filtering device. The filtering device can also bearranged in line before the crushing and/or grinding device (“in-line orserial arrangement”). If the crushing and/or grinding device isintroduced in to the tank, a part or all of the resulting suspension Spasses the crushing and/or grinding device.

Preferably at least a part of the solution leaving the filtering deviceis collected in order to obtain the aqueous solution comprising at leastone earth alkali hydrogen carbonate. However, if the observed turbidityvalue of the aqueous solution comprising at least one earth alkalihydrogen carbonate that exits the filtering device is found to be above1.0 NTU, then the aqueous solution comprising at least one earth alkalihydrogen carbonate is re-circulated in the reactor.

The water that can be used in the inventive process can be derived fromvarious sources. The water preferably treated by the process of thepresent invention is desalinated seawater, brackish water or brine,treated wastewater or natural water such as ground water, surface wateror rainfall.

According to another exemplary embodiment of the present invention, seawater or brackish water is firstly pumped out of the sea by open oceanintakes or subsurface intakes such as wells, and then it undergoesphysical pretreatments such as screening, sedimentation or sand removalprocess. Depending on the required water quality, additional treatmentsteps such as coagulation and flocculation may be necessary in order toreduce potential fouling on the membranes. The pretreated seawater orbrackish water may then be distilled, e.g., using multiple stage flash,multiple effect distillation, or membrane filtration such asultrafiltration or reverse osmosis, to remove the remaining particulatesand dissolved substances.

A flow control valve or other means may be used to control the rate offlow of carbon dioxide into the stream. For example, a CO₂ dosing blockand a CO₂ in-line measuring device may be used to control the rate ofthe CO₂ flow. According to one exemplary embodiment of the invention,the CO₂ is injected using a combined unit comprising a CO₂ dosing unit,a static mixer and an in-line CO₂ measuring device.

The carbon dioxide dose is preferably controlled by the pH of theproduced aqueous earth alkali hydrogen carbonate solution.

The alkaline aqueous suspension formed in the reactor system has asolids content in the range from 0.1 to 80 wt.-%, preferably in therange of 3 to 50 wt.-%, more preferably in the range of 5 to 35 wt.-%,based on the total weight of the resulting suspension S.

The substance comprising at least one earth alkali carbonate and theoptional at least one earth alkali hydroxide that is dosed into the tankcan be in a dry form or in an aqueous form. Preferably, the substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide has a weight median particle size (d₅₀) inthe range of 0.1 μm to 1 mm, and preferably in the range of 0.7 μm to100 μm. According to one embodiment of the present invention, thesubstance comprising at least one earth alkali carbonate is preferably aground calcium carbonate (GCC) such as marble, limestone or chalk; or adolomite.

According to another embodiment of the present invention, the substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide has a HCl insoluble content from 0.02 to 90wt.-%, preferably from 0.05 to 7 wt.-%, based on the total weight of thedry substance. The HCl insoluble content may be, e.g., minerals such asquartz, silicate, mica and/or pyrite.

According to yet another embodiment of the present invention, theaqueous suspension of the at least one substance comprising at least oneearth alkali carbonate and the optional at least one earth alkalihydroxide in a minor amount in respect to earth alkali carbonate, isfreshly prepared by mixing the water and the substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide in a minor amount in respect to earth alkali carbonate.The on-site preparation of the aqueous suspension may be preferred sincepremixed the aqueous suspensions may require the addition of furtheragents such as stabilizers or biocides, which may be unwanted compoundsin the remineralized water. According to one preferred embodiment of thepresent invention, the time period between the preparation of theaqueous suspension and the injection of the aqueous suspension is shortenough to avoid bacterial growth in the aqueous suspension. According toone exemplary embodiment, the time period between the preparation of theaqueous suspension and the injection of the aqueous suspension is lessthan 48 hours, less than 24 hours, less than 12 hours, less than 5hours, less than 2 hours or less than 1 hour. According to anotherembodiment of the present invention, the injected aqueous suspensionmeets the microbiological quality requirements specified by the nationalguidelines for drinking water.

The aqueous suspension of the at least one substance comprising at leastone earth alkali carbonate and the optional at least one earth alkalihydroxide in a minor amount in respect to earth alkali carbonate can beprepared, for example, using a mixer such as a mechanical stirrer fordilute slurries, or a specific powder-liquid mixing device for moreconcentrate slurries. Depending on the concentration of the preparedaqueous suspension the mixing time may be from 0.5 to 30 min, from 1 to20 min, from 2 to 10 min, or from 3 to 5 min. According to oneembodiment of the present invention, the aqueous suspension is preparedusing a mixing machine, wherein the mixing machine enables simultaneousmixing and dosing of the aqueous suspension.

The water used to prepare the aqueous suspension can be, e.g., distilledwater, feed water or industrial water. According to one preferredembodiment of the present invention, the water used to prepare theaqueous suspension is feed water, e.g. permeate or distillate obtainedfrom a desalination process.

According to one embodiment the aqueous solution comprising at least oneearth alkali hydrogen carbonate is injected directly into a stream offeed water. For example, a clear solution comprising earth alkalihydrogen carbonate can be injected into the feed water stream at acontrolled rate by means of a continuous conductivity measurement.

According to one embodiment, the predetermined parameter value is a pHvalue, wherein the pH value is from 6.5 to 9, preferably from 7 to 8.

FIGS. 1 and 2 are meant to illustrate the process according to thepresent invention.

FIG. 1 exemplifies one embodiment of the present invention where thefiltering device and the grinding device are arranged in a serial orin-line arrangement. The process according to the present invention ispreferably carried out in a reactor system that comprises a tank (1)that is equipped with a stirrer (2), at least one inlet (not shown) forthe water, the carbon dioxide and the at least substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide as well as a pH measuring device (not shown). The atleast one substance comprising at least one earth alkali carbonate andthe optional at least one earth alkali hydroxide in a minor amount inrespect to earth alkali carbonate can be introduced into the tank eitherin a dry or in an aqueous form. Connected to the reactor, there is atleast one filtering device (4) that has an outlet for the aqueoussolution comprising at least one earth alkali hydrogen carbonate. Whenthere is more than one filtering device present, then they can be eitherarranged in a parallel, or an in-line (serial), or a parallel and anin-line manner. The filtering device (4) is preferably a membranefilter. A grinding device (18) is arranged following the filteringdevice (4) and is also connected to the tank (1). The at least onesubstance comprising at least one earth alkali carbonate and theoptional at least one earth alkali hydroxide (6) in a minor amount inrespect to earth alkali carbonate, the water (14) and the CO₂ areintroduced into the tank (1) via the at least one inlet (not shown) andare stirred with stirrer (2) in order to obtain the resulting suspensionS having a pH of between 6 and 9. Then, the resulting suspension S isfed (8) to the filtering device (4), where coarse particles, i.e. allparticles having a size of at least 0.2 μm, that are contained in thesuspension are retained in the filtering device (4). At least a part ofthe suspension that exits the filtering device (4) is fed into thegrinding device (18), and from there it is recirculated back into tank(1). At least a part of the clear aqueous solution comprising at leastone earth alkali hydrogen carbonate is discharged (10) from thefiltering device (4).

In this embodiment, the CO₂ (20) is preferably fed into the reactorsystem before the grinding device (18), but after the filtering device(4). The grinding step provides the benefit that the (chemical) reactionspeed of the inventive process is increased by continuously producing afreshly prepared and hence active surface of the substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide. In addition, this process step decreases the size ofparticles of the substance comprising the earth alkali carbonate and theoptional at least one earth alkali hydroxide of step c), and thusenables a continuous operation of the process. The flow rate of thesuspension S through the filtering device (4) is at least 1 m/s, andpreferably in the range of 1.5 to 10 m/s, and most preferably in therange of 3 to 6 m/s. The flow rate of suspension S through the grindingdevice is 0.01 to 6 m/s, and preferably 0.1 to 0.5 m/s.

Optionally, further treatments (16) can be carried out, such as forexample a mechanical treatment or the addition of biocides or otheradditives in order to change the pH of the solution (e.g. addition of abase such as NaOH), the conductivity of the solution, or the hardness ofthe solution. As a further option, the clear aqueous solution comprisingat least one earth alkali hydrogen carbonate discharged from thefiltering device can be diluted with further water (14). The coarseparticles contained in the suspension and that are retained in thefiltering device can optionally be recirculated to the reactor in orderto be available for further conversion.

FIG. 2 exemplifies another embodiment of the present invention. Theprocess of this embodiment differs from the one of FIG. 1 in that thegrinding device (18) is not arranged following the filtering device butrather parallel to the filtering device. The grinding device (18) isconnected to the tank (1) in such way that the content of the grindingdevice (18) can be recirculated to the tank (1). A part of the resultingsuspension S having a pH of between 6 and 9 is fed (8) to the filteringdevice, whereas another part of the resulting suspension S having a pHof between 6 and 9 is fed to the grinding device (18). In thisembodiment, the CO₂ (22) is preferably fed into the reactor systembefore the grinding device (18). The ground resulting aqueous suspensionS is then circulated (24) from the grinding device (18) back to the tank(1). This grinding step provides the benefit that the (chemical)reaction speed of the inventive process is increased by continuouslyproducing a freshly prepared and hence active surface of the substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide. In addition, this process step decreases thesize of particles of the substance comprising the earth alkali carbonateand the optional at least one earth alkali hydroxide of step c), andthus enables a continuous operation of the process. The flow rate of thesuspension S through the filtering device (4) is at least 1 m/s, andpreferably in the range of 1.5 to 10 m/s, and most preferably in therange of 3 to 6 m/s. The flow rate of suspension S through the grindingdevice is 0.01 to 6 m/s, and preferably 0.1 to 0.5 m/s.

FIG. 3 exemplifies another embodiment of the present invention. Theprocess of this embodiment differs from the one of FIGS. 1 and 2 in thatthe grinding device (18) consists of grinding beads (3) that arearranged in the tank (1). Connected to the reactor, there is at leastone filtering device (4) that has an outlet for the aqueous solutioncomprising at least one earth alkali hydrogen carbonate. When there ismore than one filtering device present, then they can be either arrangedin a parallel, or an in-line (serial), or a parallel and an in-linemanner. The filtering device (4) is preferably a membrane filter. Thefiltering device (4) is connected to the tank (1) in such a way that arecirculation of a part of the suspension from the filtering device (4)into the tank (1) is possible, if required. The at least one substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide (6) in a minor amount in respect to earthalkali carbonate, the water (14) and the CO₂ are introduced into thetank (1) via the at least one inlet (not shown) and are stirred withstirrer (2) in order to obtain the resulting suspension S having a pH ofbetween 6 and 9. In this embodiment a part or all of the particles ofthe resulting suspension S are ground by the grinding beads (3) that arecontained in the tank. Then, the resulting suspension S is fed (8) tothe filtering device (4), where coarse particles, i.e. all particleshaving a size of at least 0.2 μm, that are contained in the suspensionare retained in the filtering device (4), and a clear aqueous solutioncomprising at least one earth alkali hydrogen carbonate is obtained. Atleast a part of the clear aqueous solution comprising at least one earthalkali hydrogen carbonate is discharged (10) from the filtering device(4).

Optionally, further treatments (16) can be carried out, such as forexample a mechanical treatment or the addition of biocides or otheradditives in order to change the pH of the solution (e.g. addition of abase such as NaOH), the conductivity of the solution, or the hardness ofthe solution. As a further option, the clear aqueous solution comprisingat least one earth alkali hydrogen carbonate discharged from thefiltering device can be diluted with further water (14). The coarseparticles contained in the suspension and that are retained in thefiltering device can optionally be recirculated (12) to the reactor inorder to be available for further conversion.

According to one embodiment the flow rate of the feed water is 20 000 to500 000 m³ per day.

The inventive process may be used to produce drinking water, recreationwater such as water for swimming pools, industrial water for processapplications, irrigation water, or water for the production of purifiedearth alkali carbonates.

According to one embodiment the earth alkali hydrogen carbonate solutionobtained by the inventive process has a calcium concentration from 1 to700 mg/l as CaCO₃, preferably from 50 to 650 mg/l as CaCO₃, and mostpreferred from 70 to 630 mg/l as CaCO₃. In case the slurry comprises afurther magnesium salt such as magnesium hydrogen carbonate, ormagnesium sulfate, the earth alkali hydrogen carbonate solution obtainedby the inventive process may have a magnesium concentration, asmagnesium carbonate, from 1 to 200 mg/l, preferably from 2 to 150 mg/l,and most preferably from 3 to 125 mg/l.

According to one embodiment of the present invention the earth alkalihydrogen carbonate solution has a turbidity of lower than 1.0 NTU,preferred lower than 0.3 NTU.

Examples

Specific Surface Area (SSA) of a Material

The specific surface area (SSA) was measured using a Malvern Mastersizer2000 (based on the Fraunhofer equation).

Particle Size Distribution (Mass % Particles with a Diameter <X) andWeight Median Diameter (d₅₀) of a Particulate Material

Weight median grain diameter and grain diameter mass distribution of aparticulate material were determined using a Malvern Mastersizer 2000(based on the Fraunhofer equation).

pH of an Aqueous Suspension

The pH was measured using a Mettler-Toledo pH meter. The calibration ofthe pH electrode was performed using standards of pH values 4.01, 7.00and 9.21.

Solids Content of an Aqueous Suspension

The suspension solids content (also known as “dry weight”) wasdetermined using a Moisture Analyser HR73 from the companyMettler-Toledo, Switzerland, with the following settings: temperature of120° C., automatic switch off 3, standard drying, 5 to 20 g ofsuspension.

Turbidity

The turbidity was measured with a Hach Lange 2100AN IS LaboratoryTurbidimeter and the calibration was performed using StabCal turbiditystandards (formazine standards) of <0.1, 20, 200, 1000, 4000 and 7500NTU.

Determination of the Hardness (German Hardness; Expressed in “° dH”).

The hardness refers to the total amount of earth alkali ions in theaqueous solution comprising the earth alkali hydrogen carbonate, and itis measured by complexometric titration usingethylene-diamine-tetra-actetic acid (EDTA; trade name Titriplex III) andEriochrome T as equivalent point indicator.

EDTA (chelating agent) forms with the ions Ca²⁺ and Mg²⁺ soluble, stablechelate complexes. 2 ml of a 25% ammonia solution, an ammonia/ammoniumacetate buffer (pH 10) and Eriochrome black T indicator were added to100 ml of a water sample to be tested. The indicator and the buffer isusually available as so-called “indicator-buffer tablet”. The indicator,when masked with a yellow dye, forms a red colored complex with the Ca²⁺and Mg²⁺ ions. At the end of the titration, that is when all ions arebound by the chelating agent, the remaining Eriochrome black T indicatoris in its free form which shows a green color. When the indicator is notmasked, then the color changes from magenta to blue. The total hardnesscan be calculated from the amount of EDTA that has been used.

The table below shows a conversion for the different units of the waterhardness.

Conversion for the different units of the water hardness^([1]) ° dH ° e° fH ppm mval/l mmol/l German Hardness 1° dH = 1 1.253 1.78 17.8 0.3570.1783 English Hardness 1° e = 0.798 1 1.43 14.3 0.285 0.142 FrenchHardness 1° fH = 0.560 0.702 1 10 0.2 0.1 ppm CaCO₃ (USA) 1 ppm = 0.0560.07 0.1 1 0.02 0.01 mval/l Earth alkali ions 1 mval/l = 2.8 3.51 5 50 10.50 mmol/l Earth alkali ions 1 mmol/l = 5.6 7.02 10.00 100.0 2.00 1^([1])In this regard the unit ppm is used in the meaning of 1 mg/lCaCO₃.

The carbon dioxide used in the examples is commercially available as“Kohlendioxid 3.0” from PanGas, Dagmarsellen, Switzerland. The puritywas ≥99.9 Vol.-%.

EXAMPLES

The Prior Art Examples were Prepared in the Following Way

The prior art examples show different slurries with variousconcentrations of calcium carbonate which were prepared from differentcarbonate rocks and dosed to feed water in a batch mode.

The feed water was obtained from a reverse osmosis desalination processand was acidified with about 50 mg/l CO₂. The slurries were prepared bymixing an appropriate amount of calcium carbonate with 100 ml feed waterat room temperature using a magnetic stirrer, with stirring between 1000and 1500 rpm and a mixing time of between 3 and 5 min.

The remineralization was performed by adding the slurry in small amountsto about one liter of the acidified feed water, wherein the slurry andthe feed water were mixed using a magnetic stirrer, with stirringbetween 1000 and 1500 rpm and a mixing time of 2 minutes. After everyslurry addition, a sample was taken from the treated feed water tocontrol the alkalinity, turbidity, conductivity, pH, temperature. Afinal calcium concentration of 125 mg/l as CaCO₃ was chosen as targetfor remineralization of the feed water. 125 mg CaCO₃/l represent aconcentration of 0.0125 wt.-%. For each sample the turbidity of theremineralized water was measured directly after mixing and after asettling period of minimum 60 minutes. The turbidity measured on thesettled samples was performed in order to observe the impact ofsedimentation in the remineralization process.

The turbidity was measured with a Hach Lange 2100AN IS LaboratoryTurbidimeter and the calibration was performed using StabCal turbiditystandards (formazin standards) of <0.1, 20, 200, 1000, 4000 and 7500NTU.

The total alkalinity was measured with a Mettler-Toledo T70 Titratorusing the related LabX Light Titration software. A DGi111-SG pHelectrode was used for this titration according to the correspondingMettler-Toledo method M415 of the application brochure 37 (wateranalysis). The calibration of the pH electrode was performed usingMettler-Toledo standards of pH values 4.01, 7.00 and 9.21.

Example 1—Slurry A

Two slurries having a calcium carbonate concentration of 0.5 and 5 wt.-%based on the total weight of the slurry were prepared from marble(Salses, France) derived micronized calcium carbonate having a mediumparticle size of 3.5 μm and a HCl insoluble content of 0.2 wt.-% basedon the total weight of the calcium carbonate.

The results compiled in Table 1 show similar turbidity values for bothremineralization processes with 0.5 wt.-% and 5 wt.-% CaCO₃ slurries.After a settling period, the samples presented turbidity values lowerthan 0.5 NTU.

Example 2—Slurry B

Three slurries having a calcium carbonate concentration of 0.5, 1 and 10wt.-% based on the total weight of the slurry were prepared from marble(Bathurst, Australia) derived micronized calcium carbonate having amedium particle size of 2.8 μm and a HCl insoluble content of 1.5 wt.-%based on the total weight of the calcium carbonate.

The results compiled in Table 1 show similar turbidity values for allthree remineralization processes. However the turbidity values measuredfor the settled samples taken after two minutes of remineralization arehigher than those of example 1, which may be due to the difference inthe HCl insoluble content of the marble calcium carbonate.

Example 3—Slurry C

A slurry having a calcium carbonate concentration of 5 wt.-% based onthe total weight of the slurry was prepared from limestone (Orgon,France) derived micronized calcium carbonate having a medium particlesize of 3 μm, a specific surface area (SSA) of 2.6 m²/g, and a HClinsoluble content of 0.1 wt.-% based on the total weight of the calciumcarbonate.

The results compiled in Table 1 show that the turbidity value measuredfor the settled sample is much lower in comparison to the values ofexample 1 and 2, which may be due to the different geological structuresof the carbonate rocks.

TABLE 1 Slurry Alkalinity concentration Turbidity (NTU) fresh sampleSlurry (wt.-%) Fresh sample Settled sample (mg/l CaCO₃) A 0.5 35 0.44100 A 5.0 32 0.45 120 B 0.5 26 3.90 115 B 1.0 25 3.50 112 B 10.0 24 3.30119 C 5.0 20 0.21 117

The results compiled in Table 1 show a strong turbidity of the freshsamples, and for most of the samples even after settlement.

Example 4—Different Particle Sizes

Three slurries having a calcium carbonate concentration of 5 wt.-% basedon the total weight of the slurry were prepared from marble derivedmicronized calcium carbonate having a particle size of 3.5, 9, and 20μm, respectively, and a HCl insoluble content of 0.2 wt.-% based on thetotal weight of the calcium carbonate.

The results compiled in Table 2 show that after a settling period theturbidity of the water remineralized with a larger particle size, i.e.20 μm, has a lower turbidity value in comparison with the turbidity ofthe water remineralized with smaller particle size, i.e. 3.5 μm what islogic due to the fact that the coarse particles settled much fasterversus fine particles.

TABLE 2 Mean particle size (μm) Turbidity (NTU) Alkalinity SSA (m²/g)Fresh Settled fresh sample SSA (m²/m³) sample sample (mg/l CaCO₃) 3.5 320.45 120 2.61 326 9 22 0.36 78 1.75 219 20 27 0.31 67 0.94 118

The results compiled in Table 2 show a strong turbidity for the freshsamples. After a settling period the water that was remineralized with alarger particle size, i.e. 20 μm, shows a lower turbidity value comparedto the water that was remineralized with a smaller particle size, i.e.3.5 μm, what is somehow logic due to the fact that coarse particlessettle much faster than fine ones, but which will increase the turbidityof the sample immediately if the sample is shaken.

Marble based calcium carbonate having a weight median diameter (d₅₀) of3.5 μm represents approximately a total particle surface of 2.61 m²/gcorresponding to 326.3 m²/tonne of suspension at 0.0125 wt.-% solids.

Marble based calcium carbonate having a weight median diameter (d₅₀) of9 μm represents approximately a total particle surface of 1.75 m²/gcorresponding to 218.8 m²/tonne of suspension at 0.0125 wt.-% solids.

Marble based calcium carbonate having a weight median diameter (d₅₀) of20 μm represents approximately a total particle surface of 0.94 m²/gcorresponding to 117.5 m²/tonne of suspension at 0.0125 wt.-% solids.

It can be derived from the above information that the dissolution rateof calcium carbonate is reduced by the reduced specific surface of thecalcium carbonate particles that are present in the suspension.

Examples Relating to the Invention

A general process flow sheet of the process according to the presentinvention is shown in FIGS. 1 to 3.

The feed water used in the inventive examples was obtained from an ionexchange equipment of Christ, Aesch, Switzerland Type Elite 1BTH, thefeed water having the following water specification after the ionexchanger:

Sodium 169 mg/l Calcium  2 mg/l Magnesium  <1 mg/l ° dH 0.3

The following different process routes were used to exemplify theprocess according to the present invention:

-   Process A The suspension of the reactor passes a mill with grinding    beads in the mill.

Example 5, Microdol A Extra (Dolomite)

In the present example, Microdol A extra a dolomite obtained from theCompany Norwegian Talc, Knarrevik, was used as the at least one earthalkali carbonate. The reaction and the operation conditions are given inTables 3 and 4.

Process A, 25° C. (Tank Temperature)

TABLE 3 l/h of CO₂ Permeate d₁₀ Feed ml/min at 10° dH Mem- l/h/m² d₅₀solids g/h ° dH l/h Mol brane Permeate pH d₉₀ wt.-% Mol/h PermeatePermeate CaCO₃/h pressure at 10° dH permeate SSA 15 100 32.5 40.8 133 1221 7.8 0.32 μm 11.8 0.237 1.37 μm 0.268 5.10 μm 2.85 m²/g 15 200 40 43171 2 285 7.45 23.6 0.536 0.305 15 250 50 40 200 2 332 7.25 29.5 0.670.356

The total mineral surface of the particles in the suspension of thistrial represents 427 500 m²/tonne of suspension.

Process A, 40° C. (Tank Temperature)

TABLE 4 l/h of CO₂ Permeate d₁₀ Feed ml/min at 10° dH Mem- l/h/m² d₅₀solids g/h ° dH l/h Mol brane Permeate pH d₉₀ wt.-% Mol/h PermeatePermeate CaCO₃/h pressure at 10° dH permeate SSA 8 100 38 74 280 1 4677.7 0.32 μm 11.8 0.499 1.26 μm 0.268 3.72 μm 2.93 m²/g

The total mineral surface of the particles in the suspension of thistrial represents 167 428 m²/tonne of suspension.

The ratio of produced mol CaCO₃ to used mol CO₂ in this example is1:0.54

Example 6, Marble

In the present example, a marble sold under the trade name “Omyacarb 10AV” from the company Omya International, Switzerland, was used as theearth alkali carbonate. The HCL insoluble content was 0.7 wt.-%. Thereaction and the operation conditions are given in Table 5.

Process A, 24° C. (Tank Temperature)

TABLE 5 l/h of CO₂ Permeate d₁₀ Feed ml/min at 10° dH Mem- l/h/m² d₅₀solids g/h ° dH l/h Mol brane Permeate pH d₉₀ wt.-% Mol/h PermeatePermeate CaCO₃/h pressure at 10° dH permeate SSA 15 50 40 41 166 1.5 2776.7 0.33 μm 5.9 0.296 1.33 μm 0.134 4.50 μm 2.81 m²/g

The total mineral surface of the particles in the suspension of thistrial represents 421 500 m²/tonne of suspension

The ratio of produced mol CaCO₃ to used mol CO₂ in this example is1:0.45

Use of Aqueous Solution Comprising Calcium Hydrogen Carbonate for theProduction of Precipitated Calcium Carbonate

2 liters of clear permeate obtained according to process B in thisExample were heated for 2 h at 70° C., and the resulting precipitate wascollected by filtering using a membrane filter having a pore size of 0.2μm.

The XRD analysis of the resulting precipitate shows the following:

Aragonitic precipitated calcium carbonate (PCC) 85.8 wt.-% Magnesiumrich calcitic precipitated calcium carbonate 14.2 wt.-% Silica/Silicates<0.1 wt.-%

Hence, the XRD result shows that very clean precipitated calciumcarbonate can be prepared out of silicate contaminated raw material.

Example 7, Marble/Silcate Blend, Austria

In the present example, a marble/silicate blend (Omyacarb 10 AV″ fromthe company Omya International, Switzerland, mixes with 7% mica from thecompany Aspanger Kaolin, Austria) was used as the starting material. TheHCL insoluble content was 7.5 wt. % (mainly mica). The reaction and theoperation conditions are given in Table 6.

Process A, 24° C. (Tank Temperature)

TABLE 6 l/h of CO₂ Permeate d₁₀ Feed ml/min at 10° dH Mem- l/h/m² d₅₀solids g/h ° dH l/h Mol brane Permeate pH d₉₀ wt.-% Mol/h PermeatePermeate CaCO₃/h pressure at 10° dH permeate SSA 5 250 35 65 226 2 3776.8 0.30 μm 29.5 0.403 1.18 μm 0.67 6.16 μm 3.07 m²/g

The total mineral surface of the particles in the suspension of thistrial represents 153 500 m²/tonne of suspension.

The ratio of produced mol CaCO₃ to used mol CO₂ in this example is1:1.66.

This example clearly demonstrates that the present invention can also becarried out with highly impure starting products (in this case theimpurity is mica). This is a cost efficient alternative to processeswhere only pure starting products can be used and might have to beshipped to the production site from far away.

Use of Aqueous Solution Comprising Calcium Hydrogen Carbonate for theProduction of Precipitated Calcium Carbonate

2 liters of clear permeate obtained according to process B in thisexample were heated for 2 h at 70° C., and the resulting precipitate wascollected by filtering using a membrane filter having a pore size of 0.2μm.

The XRD analysis of the resulting precipitate shows the following:

Aragonitic PCC 97.3 wt.-% Magnesium rich calcitic PCC  2.7 wt.-%Silica/Silicates <0.1 wt.-%

Hence, the XRD result shows that very clean precipitated calciumcarbonate is obtained from a starting product that contains an insolublecontent (impurities) of 7.5 wt.-%.

Example 8, Half Burned Dolomite

Process A=passing the mill with grinding beats in the mill, T=20° C.

Ground and partially burned German Dolomite with a mean particle size of7.5 μm and a specific surface area (SSA) of 0.90 m²/g from DolomitwerkJettenberg, Schöndorfer GmbH, Oberjettenberg, was dispersed in feedwater (ion exchange equipment from Christ) at a solids content of 2wt.-%. The resulting suspension had a conductivity of 1 104 μS/cm.

The suspension was pumped in a circulation mode at a rate of 2200 l/hand at a temperature of 20° C. from the reactor passing 3 membranemodules of 0.2 m² each (Microdyn-Modul MD 063 TP 2N) and was pumped backinto the reactor. The membrane modules were arranged in a serial line.

Every 15 minutes samples were taken from the suspension and theconductivity, the German hardness as well as the pH of the samples wasdetermined. Table 7 lists the obtained results.

TABLE 7 CO₂ Amount of Con- Time addition Temp permeate ductivityHardness [min] [ml/min] [° C.] [g/15 min] [μS/cm] [° dH] pH 0 50 18.0 1550 19.0 11635.6 1029 15.0 10.96 30 50 19.5 5098.7 1108 20.0 10.45 45 5019.5 7418 1160 27.5 10.54 60 200 20.0 7940 1195 30.0 10.58 75 200 20.07464.9 1311 37.5 10.45 90 500 20.0 7992 1445 50.0 10.28 105 500 20.08039.4 1716 75.0 10.11 120 500 20.0 7704.3 1969 95.0 9.99 135 500 20.07932.3 2090 120.0 9.92 150 750 20.0 7996.4 2220 120.0 9.82 165 750 20.57949.2 2580 145.0 9.59 180 750 20.5 8028.2 2820 160.0 9.45 195 750 20.58114.3 3030 165.0 9.28 210 750 20.5 8217.9 3250 165.0 9.10 225 750 21.08188.1 3550 150.0 8.78 240 500 21.0 8512.6 3580 135.0 8.63 255 500 21.08177.7 3610 135.0 8.36 270 500 22.0 9901.2 3670 135.0 7.94 285 500 22.57790.3 3660 125.0 7.55

Table 7 shows a pH below 9.5 and stable conditions with respect to theconductivity after 3 to 3.5 hours.

Table 8 lists the ion chromatography (882 Compact IC Plus, Metrohm)results of the samples taken after 15, 90, 120, 195 and 285 minutes.

TABLE 8 Sample taken after Calcium Magnesium x minutes [ppm]^([1])[ppm]^([2]) 15 3 72 90 11 232 120 23 446 195 34 630 285 20 561 ^([1])Inthis regard the unit ppm is used in the meaning of 1 mg/l CaCO₃.^([2])In this regard the unit ppm is used in the meaning of 1 mg/l MgCO₃

Table 8 also shows stable conditions with respect to the magnesiumcontent after 3 to 3.5 hours.

Table 9 lists the reaction conditions used as well as the pH, thehardness, the d₁₀, the d₅₀, the d₉₀ and the specific surface area (SSA)of the samples taken after 15, 90, 120, 195 and 285 minutes. Samplinglocation was the tank, and the pH value of the permeate was determinedby titration.

TABLE 9 l/h of Sample Permeate d₁₀ taken Feed at 10° dH Mem- l/h/m² d₅₀after x solids CO₂ ° dH Mol brane Permeate pH d₉₀ min wt.-% ml/minPermeate CaCO₃/h pressure at 10° dH permeate SSA 15 1.77 50 15 69.8 0116 10.2 1.03 μm 0.124 7.51 μm 16.57 μm 0.899 m²/g 90 1.60 500 50 159.80 266 10.3 1.03 μm 0.285 5.24 μm 10.88 μm 0.959 m²/g 120 1.66 500 95292.8 0 488 10.0 0.46 μm 0.521 2.64 μm 15.56 μm 1.853 m²/g 195 1.45 750165 535.5 0 893 9.3 0.33 μm 0.953 2.20 μm 24.43 μm 2.524 m²/g 285 1.26500 125 389.5 0 649 7.6 0.24 μm 0.693 0.74 μm 2.50 μm 4.268 m²/g

At the beginning the total particle surface in the suspension of thistrial represents 15 912 m²/tonne of suspension, and the medium diameter(d₅₀) was determined to be 7.5 μm. After 195 minutes the medium diameter(d₅₀) was determined to be 0.74 μm, and the total particle surface inthe suspension represented 126 000 m²/tonne of suspension.

Use of Aqueous Solution Comprising Calcium Hydrogen Carbonate for theProduction of Precipitated Calcium Carbonate

2 liter of clear permeate sampled after 285 minutes were heated for 2 hat 70° C. and the resulting precipitate (P) was collected by filteringusing a membrane filter of 0.2 μm pore size and was analyzed by XRD. Thefiltrate was evaporated and dried and the residue (R) was analyzed byXRD.

The XRD analysis of the resulting precipitate as well as of the obtainedresidue shows the following:

Hydromagnesite Northupite Aragonite Halite Sample AmorphousMg₅(CO₃)₄(OH)₂(H₂O)₄ Na₃Mg(CO₃)₂Cl CaCO₃ NaCl P X X x R X X X X x

Example 9—PCC Langenau

In this trial precipitated calcium carbonate (PCC) was used.

The PCC was produced by adding a 0.1 wt.-% solution of portlandite totap water of 25° dH to increase the pH of the water from pH 6.4 to pH7.8. The so obtained precipitated CaCO₃ was used for this trial.

Process A, 20° C. (Tank Temperature)

l/h of CO₂ Permeate d₁₀ Feed ml/min at 10° dH Mem- l/h/m^(2 of) d₅₀solids g/h ° dH of l/h of Mol brane Permeate pH of d₉₀ Wt.-% Mol/hPermeate Permeate CaCO₃/h pressure at 10° dH permeate SSA 2 200 25 36.290.6 0 151 7.0 0.30 μm 23.6 0.16 0.87 μm 0.54 3.89 μm 3.57 m²/g

The total mineral surface of the particles in the suspension of thistrial represents 71 400 m²/tonne of suspension.

The ratio of produced mol CaCO₃ to used mol CO₂ in this example is1:3.38.

Example 10—Dolomite/Limestone Blend

Pilot Plant Trial

In the present example, one part Microdol A extra a dolomite asdescribed in Example 5 was mixed with two parts of limestone of theregion of Avignon, France, and was used as the blend of earth alkalicarbonates.

The goal of the trial in Example 10 was to produce a solution of earthalkali hydrogen carbonate of a pH of 6.5 to 6.7 in pilot scale.

The blend of earth alkali carbonates had a d₁₀ of 0.43 μm, a d₅₀ of 2.43μm and a d₉₀ of 6.63 μm at the beginning of the trial.

The blend was fed as 50 wt.-% suspension in water.

The reaction and operation conditions are given below.

Process A=passing the mill with grinding beats in the mill, tanktemperature T=18.5° C.

Feed tank volume: 1.0 m³

Feed water: deionized water obtained from an ion exchange equipment ofChrist, Aesch, Switzerland, (<1 mg/l earth alkali carbonate).

Cross flow polyethylene membrane module of 8.0 m², inner diameter 5.5mm, 3 m long, 174 tubes in parallel. (Seprodyn filter module SE 150 TP1L/DF, Microdyn). Pore diameter 1.0 μm.

Feed flow of suspension S to the cross flow membrane unit: 36 m³/h,speed across the membranes: 3 m/s.

Pressure at the cross flow membrane inlet: 1 bar

Pressure at the cross flow membrane outlet: 0.3 bar

Pressure at the solution outlet: 0.05 bar

Feed flow of suspension S to the dividing device: 0.40 m³/h

Pressure at the mill inlet: 0.7 to 0.8 bar

Dose of CO₂: 1.0 liter/min at a pressure of 1.5 to 1.6 bar.

Feed solids of suspension S: 15 wt.-%

Results measured at 44 hours continuous running:

Earth alkali d₁₀ ion concen- m³/h of l/h/m² d₅₀ ° dH m³/h tration inPermeate Permeate pH d₉₀ Permeate Permeate the permeate at 10° dH at 10°dH permeate SSA 33 0.5 Ca²⁺: 214 mg/l 1.65 0.21 6.7 0.34 μm Mg²⁺: 20mg/l 1.47 μm 4.11 μm 2.72 m²/g

The specific particle surface of the suspension S obtained according tothe inventive process and taken after 44 hours was 408000 m²/tonne ofsuspension S.

A first quality of tap water comprising 45 mg/l earth alkali carbonate(sum of CaCO₃/MgCO₃) was produced by diluting the permeate of this trialwith feed water. The resulting capacity of this trial corresponds toapproximately 6.7 m³/h at a concentration of 45 mg/l earth alkalicarbonate.

A second quality of tap water comprising 100 mg/l earth alkali carbonate1 (CaCO₃) and 10-15 mg/l of earth alkali carbonate 2 (MgCO₃) wasproduced by diluting the permeate of this trial with feed water. Theresulting capacity of this trial corresponds to approximately 2.7 m³/hat a concentration of 100 mg/l CaCO₃ and 10-15 mg/l MgCO₃.

Example 11, Further Pilot Plant Trials

This example presents further trials for the preparation of aqueoussolutions of calcium hydrogen carbonate in pilot scale. The obtainedsolution of calcium hydrogen carbonate is then used for theremineralization of soft water, which could be for instance natural softwater from ground water or surface water sources, desalinated water fromreverse osmosis or distillation, rain water. The trials were performedusing different calcium carbonate products as raw material for thepreparation of calcium carbonate suspension, hereafter slurries, and theresulting solutions of calcium hydrogen carbonate obtained after thedosing of carbon dioxide.

The following Table 10 summarizes the properties of the calciumcarbonate used during the remineralization pilot trials with an initialslurry volume of 1200 L.

TABLE 10 Calcium carbonate d₅₀ CaCO₃ HCl insoluble Sample^([1]) rock[μm] [wt.-%] [wt.-%] A Marble 13.7 96.6 0.6 ^([1])It has to be notedthat the above listed calcium carbonate is commercially available fromOmya, Switzerland.

The following Table 11 summarizes the properties of the slurries of thecalcium carbonate product that have been used for the present trials.

TABLE 11 Starting slurry composition Target slurry Mean particle size(μm) concentration SSA (m²/g) Slurry Product (%) Expected total SSA(m²/m³) 1 A 10 13.7 1.33 160 2 A 2 13.7 1.3 32

The in Table 11 mentioned calcium carbonate suspensions (or “slurries”)were prepared by mixing the micronized calcium carbonate powder andreverse osmosis water (RO water). The RO water was produced on-siteusing a reverse osmosis unit and had the average quality as outlined inthe following Table 12.

TABLE 12 Conductivity Turbidity pH (μS/cm) (NTU) RO water 6.4-6.6 10-25<0.1

The tank was filled up completely with the respective calcium carbonatesuspension. Then, the calcium carbonate suspension was pumped from thetank towards the mill, and from there to the membrane filtering devicefor filtration. The mill was used as dosing point for the carbon dioxidethat is required for the dissolution of the calcium carbonate into thewater. The obtained dissolved hydrogen carbonate then passed through themembrane, while the undissolved calcium carbonate was fed back to thetank. Amongst different water parameters, the conductivity was used as aproxy for measuring the amount of dissolved hydrogen carbonate obtainedby this process.

The conditions for the carbon dioxide and calcium carbonate dosing canbe derived from Table 13.

TABLE 13 Target CO₂/ Target CO₂/CaCO₃ concentrate Concentrateconcentration CO₂ stoechiometric ratio flowrate (mg/L as flowrate ratio(L CO₂/L (L/h) CaCO₃) (L/min) (x-fold) concentrate) 500 500 5 5 0.6

The following Table 14 summarizes the results obtained at the end of thefirst and second day of testing (6-7 hours per day) of slurry 2 (with aslurry having a solids content of 2 wt.-% of sample A).

TABLE 14 Final Start Final d50% Testing SSA_(f) Total SSA conductivityTest Slurry start days [slurry]_(f) d50%_(f) (m²/g) (m²/t) (μS/cm) 1Slurry 2 13.7 1 1.9% 4.0 2.4 45′600 1187 2 Slurry 2 13.7 2 1.8% 3.6 2.646′800 1169

The results presented in Table 15 were performed using slurry 1: ˜10 wt.% of sample A. The test was performed using the same CO₂ dosing ratio of0.3 L CO₂/L concentrate and the results presented the values obtained atthe end of a full day of testing.

TABLE 15 Final Start Final d50% Testing SSA_(f) total SSA_(f)conductivity Test Slurry start days [slurry]_(f) (m²/g) (m²/t) (μS/cm) 3Slurry 1 13.7 1 9.5% 2.8 266′000 750Impact of the CO₂ Excess Ratio

In addition to the surface area of the solids present in the slurry itis expected that the stoichiometric ratio of carbon dioxide compared tocalcium carbonate, i.e. measured as CO₂ flowrate/concentrate flowrate,also impacts the dissolution of the calcium carbonate into the water.Therefore the final concentration of the dissolved hydrogen carbonate,measured as final conductivity, should increase proportionally to theCO₂ stoechiometric excess dosed in the slurry. The results presented intable 16 were performed using two slurries both made of Sample A(d₅₀=13.7 μm, SSA=1.3 m²/g) with slurry 1 starting with a higher solidcontent (slurry 1: ˜10 wt %) and slurry 2 starting with a lower solidcontent (slurry 2: ˜2 wt. The carbon dioxide and the concentrateflowrates were adjusted in order to reach the target stoichiometricCO₂/CaCO₃ ratio of 1-, 2.5- and 5-fold, respectively the CO₂ flowrateratio of 0.12, 0.3 and 0.6 L CO₂/L concentrate.

TABLE 16 Process Final CO2 flowrate Final ratio (L CO₂/L Start TestingSSA_(f) total SSA_(f) conductivity Test concentrate) Slurry days[slurry]_(f) d50%_(f) (m²/g) (m²/t) (μS/cm) 4 0.12 Slurry 1 1  11.0% *3.7 2.6 286′000 570 3 0.3 Slurry 1 1 9.5% 3.4 2.8 266′000 750 2 0.6Slurry 2 2 1.8% 3.6 2.6  46′800 1169 1 0.6 Slurry 2 1 1.9% 4.0 2.4 45′600 1187 * estimated value

The outcome of this set of trials shows that the conductivity isincreasing proportionally to the target stoichiometric CO₂/CaCO₃ ratiomeasured as L CO₂/L concentrate.

The invention claimed is:
 1. A process for the preparation of an aqueoussolution comprising at least one earth alkali hydrogen carbonate, theprocess comprising the steps of: a) providing water, b) providing atleast one substance comprising at least one earth alkali carbonate andoptionally at least one earth alkali hydroxide, the at least onesubstance being in a dry form or in an aqueous form, c) providing CO₂,d) combining in a reaction tank either: (i) the water of step a), the atleast one substance comprising at least one earth alkali carbonate andthe optional at least one earth alkali hydroxide of step b) and the CO₂of step c), or (ii) the water of step a) and the at least one substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide of step b) in order to obtain an alkalineaqueous suspension of the at least one substance comprising at least oneearth alkali carbonate and the optional at least one earth alkalihydroxide, and subsequently combining the alkaline aqueous suspensionwith the CO₂ of step c), in order to obtain a resulting suspension Shaving a pH of between 6 and 9, the resulting suspension S containingparticles, e) filtering at least a part of the resulting suspension S bypassing at least a part of the resulting suspension S through afiltering device in order to obtain an aqueous solution comprising atleast one earth alkali hydrogen carbonate, wherein the aqueous solutionobtained after filtration has a turbidity value of lower than 1 NTU anda calcium concentration, as calcium carbonate, from 50 to 650 mg/l, f)subjecting at least a part or all of the particles of the resultingsuspension S to a grinding and/or crushing step to obtain a suspensioncomprising ground particles at least part of the ground particles beingintroduced into the tank of step d), wherein step f) takes place afterstep d) and before and/or parallel to and/or after step e), wherein theparticles of the resulting suspension S obtained in step d) represent atotal particle surface area (SSA_(total)) that is at least 1000 m²/tonneof the resulting suspension S, wherein the resulting suspension Sobtained in step d) has a solids content in the range from 1 to 35 wt.%, based on the total weight of the resulting suspension S, wherein theat least one substance comprising at least one earth alkali carbonateand the optional at least one earth alkali hydroxide of step b) ismarble, limestone, chalk, half burnt lime, burnt lime, dolomiticlimestone, calcareous dolomite, half burnt dolomite, burnt dolomite, aprecipitated earth alkali carbonate, or precipitated calcium carbonate,and wherein the at least one substance comprising at least one earthalkali carbonate and the optional at least one earth alkali hydroxide ofstep b) has a weight median particle size (d₅₀) in the range of 0.1 μmto 1 mm, with the proviso that an addition of the CO₂ of step c) doesnot take place before an addition of the at least one substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide of step b).
 2. The process according to claim1, wherein the particles of the resulting suspension S represent a totalparticle surface area (SSA_(total)) that is in the range of5000-5,000,000 m²/tonne of the resulting suspension S.
 3. The processaccording to claim 1, wherein the particles of the resulting suspensionS represent a total particle surface area (SSA_(total)) that is in therange of 10,000-5,000,000 m²/tonne of the resulting suspension S.
 4. Theprocess according to claim 1, wherein the particles of the resultingsuspension S represent a total particle surface area (SSA_(total)) thatis in the range of 70,000-5,000,000 m²/tonne of the resulting suspensionS.
 5. The process according to claim 1, wherein the at least onesubstance comprising at least one earth alkali carbonate and theoptional at least one earth alkali hydroxide of step b) has a specificsurface area (SSA) in the range of 0.01 to 200 m²/g.
 6. The processaccording to claim 1, wherein the at least one substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide of step b) has a specific surface area (SSA) in therange of 1 to 100 m²/g.
 7. The process according to claim 1, wherein theat least one substance comprising at least one earth alkali carbonateand the optional at least one earth alkali hydroxide of step b) has ahydrochloric acid (HCl) insoluble content from 0.02 to 90 wt. %, basedon the total weight of the dry substance.
 8. The process according toclaim 1, wherein the at least one substance comprising at least oneearth alkali carbonate and the optional at least one earth alkalihydroxide of step b) has a hydrochloric acid (HCl) insoluble contentfrom 0.05 to 15 wt. %, based on the total weight of the dry substance.9. The process according to claim 1, wherein the water of step a) isdistilled water, tap water, desalinated water, brine, wastewater, groundwater, surface water or rainfall.
 10. The process according to claim 1,wherein the CO₂ of step c) is gaseous carbon dioxide, liquid carbondioxide, solid carbon dioxide, or a gaseous mixture of carbon dioxideand at least one other gas.
 11. The process according to claim 1,wherein the CO₂ of step c) is gaseous carbon dioxide.
 12. The processaccording to claim 1, wherein the amount of CO₂ used, in mol, to produce1 mol of the at least one earth alkali hydrogen carbonate in the aqueoussolution is in the range of 0.5 to 4 mol of CO₂.
 13. The processaccording to claim 1, wherein the amount of CO₂ used, in mol, to produce1 mol of the at least one earth alkali hydrogen carbonate in the aqueoussolution is in the range of 0.5 to 2.5 mol of CO₂.
 14. The processaccording to claim 1, wherein the amount of CO₂ used, in mol, to produce1 mol of the at least one earth alkali hydrogen carbonate in the aqueoussolution is in the range of 0.5 to 1.0 mol of CO₂.
 15. The processaccording to claim 1, wherein the amount of CO₂ used, in mol, to produce1 mol of the at least one earth alkali hydrogen carbonate in the aqueoussolution is in the range of 0.5 to 0.65 mol of CO₂.
 16. The processaccording to claim 1, wherein the aqueous solution comprising at leastone earth alkali hydrogen carbonate that is obtained in step e) or stepf) has a hardness from 5 to 130° dH.
 17. The process according to claim1, wherein the aqueous solution comprising at least one earth alkalihydrogen carbonate that is obtained in step e) or step f) has a hardnessfrom 10 to 60° dH.
 18. The process according to claim 1, wherein theaqueous solution comprising at least one earth alkali hydrogen carbonatethat is obtained in step e) or step f) has a hardness from 15 to 50° dH.19. The process according to claim 1, wherein the aqueous solutioncomprising at least one earth alkali hydrogen carbonate that is obtainedin step e) or step f) has a pH in the range of 6.5 to 9 at 20° C. 20.The process according to claim 1, wherein the aqueous solutioncomprising at least one earth alkali hydrogen carbonate that is obtainedin step e) or step f) has a pH in the range of 6.7 to 7.9 at 20° C. 21.The process according to claim 1, wherein the aqueous solutioncomprising at least one earth alkali hydrogen carbonate that is obtainedin step e) or step f) has a pH in the range of 6.9 to 7.7 at 20° C. 22.The process according to claim 1, wherein the aqueous solutioncomprising at least one earth alkali hydrogen carbonate that is obtainedin step e) has a calcium concentration, as calcium carbonate, from 70 to630 mg/l.
 23. The process according to claim 1, wherein the aqueoussolution comprising at least one earth alkali hydrogen carbonateobtained in step e) has a magnesium concentration, as magnesiumcarbonate, from 1 to 200 mg/l.
 24. The process according to claim 1,wherein the aqueous solution comprising at least one earth alkalihydrogen carbonate obtained in step e) has a magnesium concentration, asmagnesium carbonate, from 2 to 150 mg/l.
 25. The process according toclaim 1, wherein the aqueous solution comprising at least one earthalkali hydrogen carbonate obtained in step e) has a magnesiumconcentration, as magnesium carbonate, from 3 to 125 mg/l.
 26. Theprocess according to claim 1, wherein the aqueous solution comprising atleast one earth alkali hydrogen carbonate obtained in step e) has aturbidity value of lower than 0.5 NTU.
 27. The process according toclaim 1, wherein the aqueous solution comprising at least one earthalkali hydrogen carbonate obtained in step e) has a turbidity value oflower than 0.3 NTU.
 28. The process according to claim 1, wherein atleast step d) is carried out at a temperature that is in a range of 5 to55° C.
 29. The process according to claim 1, wherein at least step d) iscarried out at a temperature that is in a range of 20 to 45° C.
 30. Theprocess according to claim 1, which is a continuous process.
 31. Theprocess according to claim 1, wherein the filtering device of step e) isa membrane filter or a tube membrane filter with a pore size of between0.02 μm and 0.2 μm.
 32. A process for the mineralization of watercomprising the following steps: a) providing feed water, b) providingthe aqueous solution comprising at least one earth alkali hydrogencarbonate obtained from the process of claim 1, and c) combining thefeed water of step a) and the aqueous solution comprising at least oneearth alkali hydrogen carbonate of step b) in order to obtainmineralized water.
 33. The process according to claim 32, wherein theaqueous solution comprising at least one earth alkali hydrogen carbonateof step b) has a hardness that is at least 3° dH higher than thehardness of the feed water of step a).
 34. The process according toclaim 32, wherein the aqueous solution comprising at least one earthalkali hydrogen carbonate of step b) has a hardness that is at least 5°dH higher than the hardness of the feed water of step a).
 35. Theprocess according to claim 32, wherein the aqueous solution comprisingat least one earth alkali hydrogen carbonate of step b) has a hardnessof at least 15° dH.
 36. A process for the production of a precipitatedearth alkali carbonate, the process comprising the following steps: a)providing the aqueous solution comprising at least one earth alkalihydrogen carbonate obtained by the process of claim 1, and b) heatingthe aqueous solution comprising the at least one earth alkali hydrogencarbonate of step a) in order to obtain the precipitated earth alkalicarbonate, and/or c) adding at least one earth alkali hydroxide or earthalkali oxide to the solution of step a) to obtain the precipitated earthalkali carbonate, wherein the precipitated earth alkali carbonate is aprecipitated calcium carbonate and/or hydromagnesite.